1. Field of the Invention
This invention relates to a printing apparatus for printing quarter em-size letters with a high print quality.
2. Description of Related Art
Most of printing apparatuses which are presently used have a resolution of 300 DPI. However, it is expected, from the viewpoint of the improvement of print quality, that printing apparatuses having higher resolution, for example 600 DPI, will become dominant in the near future. Most of these printing apparatuses, such as laser printers for carrying out a printing operation with 600 DPI resolution, are so designed that the resolution is switchable between 600 DPI and 300 DPI to permit printing of print data which is set in 300 DPI resolution. Some of these laser printers, which are capable of printing print data of both 600 DPI and 300 DPI resolution, are equipped with font data for 600 DPI and font data for 300 DPI. Other laser printers are equipped with only the font data for 600 DPI to reduce required memory capacity for font data.
For a printing operation of a special-size letter other than the em-size (standard size) letters, such as a lateral double em-size letter, which is obtained by doubly enlarging the lateral, or horizontal, size of an em-size letter while keeping its vertical size; a vertical double em-size letter which is obtained by doubly enlarging the vertical size of an em-size letter while keeping its lateral or horizontal size; a quadruple em-size letter which is obtained by doubly enlarging both of the lateral or horizontal size and the vertical size of an em-size letter; or a quarter em-size letter which is obtained by reducing each of the lateral or horizontal size and the vertical size of an em-size letter to half size, font data which are exclusively used for these special size letters are not equipped with the laser printers for the purpose of suppressing memory capacity for the whole font data. Accordingly, in order to obtain these special size letters in a laser printer, the font data for letters of each size are prepared using font data for em-size letters which are stored in the laser printer and a printing operation of desired-size letters is carried out on the basis of the prepared font data.
For the preparation of the font data for special-size letters from the font data for em-size letters, the font data for letters whose size is larger than the em-size can be relatively easily prepared by enlarging the dot interval of dot arrays constituting the em-size letters in a desired enlarging direction, for example, by doubly enlarging the vertical dot interval when vertical double em-size letters are required to be obtained.
However, for the preparation of the font data for quarter em-size letters, whose size is smaller than the em-size, a complicated processing is required in addition to the above size altering processing. That is, half of vertically- or horizontally-arranged, that is, laterally-arranged dots, (hereinafter referred to as "vertical and lateral dots") which constitute the font data for em-size letters are first thinned out, and then a size-altering processing in which each of the vertical and lateral sizes is reduced to its half size is carried out to thereby prepare the font data for quarter em-size letters. Through this thinning processing, for example, there occurs a problem that two separated portions of "Kanji" are contacted with each other, or the apex of a triangle at an upper portion of a capital letter "A" is blurred. In order to solve this problem, a repairing processing for repairing a letter-unclarified (damaged) portion is executed in accordance with a well-known algorithm. This repairing processing requires a long time. In addition, even if the letter repairing processing using the well-known algorithm is conducted, a beautiful face (letter style) cannot be obtained by the font data for quarter em-size letters which are obtained by reducing the em-size letters, and thus there occurs a problem that the letters appear to be battered.